Poly(isobutylene-co-isoprene), or IIR, is a synthetic elastomer commonly known as butyl rubber which has been prepared since the 1940's through the random cationic copolymerization of isobutylene with small amounts of isoprene (1-5 mole %). As a result of its molecular structure, IIR possesses superior air impermeability, a high loss modulus, oxidative stability and extended fatigue resistance.
Butyl rubber is understood to be a copolymer of an isoolefin and one or more, preferably conjugated, multiolefins as comonomers. Commercial butyl comprises a major portion of isoolefin and a minor amount, usually not more than 2.5 mol %, of a conjugated multiolefin. Butyl rubber or butyl polymer is generally prepared in a slurry process using methyl chloride as a diluent and a Friedel-Crafts catalyst as part of the polymerization initiator. This process is further described in U.S. Pat. No. 2,356,128 and Ullmanns Encyclopedia of Industrial Chemistry, volume A 23, 1993, pages'288-295.
Halogenation of this butyl rubber produces reactive allylic halide functionality within the elastomer. Conventional butyl rubber halogenation processes are described in, for example, Ullmann's Encyclopedia of Industrial Chemistry (Fifth, Completely Revised Edition, Volume A231 Editors Elvers, et al.) and/or “Rubber Technology” (Third Edition) by Maurice Morton, Chapter 10 (Van Nostrand Reinhold Company © 1987), particularly pp. 297-300.
The presence of allylic halide functionalities allows for nucleophilic alkylation reactions. It has been recently shown that treatment of brominated butyl rubber (BIIR) with nitrogen and/or phosphorus based nucleophiles, in the solid state, leads to the generation of IIR-based ionomers with interesting physical and chemical properties (see: Parent, J. S.; Liskova, A.; Whitney, R. A; Resendes, R. Journal of Polymer Science, Part A: Polymer Chemistry 43, 5671-5679, 2005; Parent, J. S.; Liskova, A.; Resendes, R. Polymer 45, 8091-8096, 2004; Parent, J. S.; Penciu, A.; Guillen-Castellanos, S. A.; Liskova, A.; Whitney, R. A. Macromolecules 37, 7477-7483, 2004). The ionomer functionality is generated from the reaction of a nitrogen or phosphorous based nucleophile and the allylic halide sites in the halogenated butyl rubber to produce a ammonium or phosphonium ionic group respectively. The physical properties of these halogenated butyl based ionomers, such as green strength, modulus, filler interactions etc., are superior to those of their non-ionomeric counterpart.
It has been discovered that the addition of para-methylstyrene to the mixed feed of butyl polymerizations (MeCl, IB and IP mixed feed, with AlCl3/H2O as initiator) results in a high molecular weight polymer with up to 10 mol % of styrenic groups randomly incorporated along the polymer chain (See: U.S. Pat. No. 6,960,632; Kaszas et al. Rubber Chemistry and Technology, 2001, 75, 155). The incorporation of para-methylstyrene is found to be uniform throughout the molecular weight distribution due to the similarity in reactivity with isobutylene. The isoprene moieties within the butyl terpolymers can be halogenated by conventional methods leading to similar Type II and Type III allylic halide structures as the current LANXESS halobutyl grades.
Alternatively, a butyl copolymer may comprise a C4-C7 isomonoolefin, such as isobutylene, and a comonomer, such as para-alkylstyrene, preferably para-methylstrene. When halogenated, some of the alkyl substituent groups present in the styrene monomer units contain a benzylic halogen. Additional functional groups can be incorporated by nucleophilic displacement of the benzylic halogen with a variety of nucleophiles as described in U.S. Pat. No. 5,162,445. Use of tertiary amines and phosphines results in the formation of butyl ionomers based on these copolymers with improved physical properties.
Conventional butyl polymers, including halobutyl, suffer from the disadvantage that, in order to take full advantage of their properties, they need to be crosslinked though curing or vulcanization. However, once the covalent crosslinks are formed through conventional methods (ie. vulcanization), the polymer compounds are no longer reprocessable or remoldable and any leftover material formed in manufacturing is of no use to the manufacturer, must be disposed of, and can be a significant cost to the manufacturer.
Various investigations have been initiated into producing polymers, namely ionic polymers, which behave similar to covalently crosslinked polymers at room temperature but at higher temperatures, are readily remoldable. This is achievable as ionic polymers are crosslinked via ionic bonding versus covalent bonding as in normal vulcanized rubbers. Ionic bonds, or clusters, are known to be disrupted by the action of shear or heat, while the covalent bonds of more conventional cure systems (vulcanization) are essentially permanent links between polymer chains.
U.S. Pat. No. 3,646,166 describes a method to introduce carboxylic acid groups into a butyl rubber backbone. This is accomplished in a multistep solution reaction of dehalogenation of halobutyl to form a conjugated diene, followed by reaction with maleic anhydride which is then hydrolyzed and reacted with a metallic salt or amine to form an ionic polymer that could be remolded with good physical properties.
U.S. Pat. No. 3,898,253 describes a remoldable butyl rubber composition formed by first combining a halobutyl rubber with selected filler (silica, talc or calcium carbonate) on a warmed mill followed by the addition of an alkyl tertiary amine on a cooled mill and then molded in a press at 175° C. to allow the amine to react with the rubber. The resulting compound was then re-heated on the mill at 175° C., and re-molded resulting in compounds that retained some physical properties however in most cases, these physical properties were reduced by at least half.
U.S. Pat. Nos. 4,102,876 and 4,173,695 describe the formation of ionomers based on EPDM and low molecular weight butyl formed via a multistep process in which sulfonation of the polymer occurs followed by quaternization with phosphonium or ammonium compounds. The resulting ionomers have the anionic group attached to the backbone and the cationic group as the counterion.
The examples outlined above, while displaying remoldable properties suffer from disadvantages related to long production times to form the remoldable polymer (U.S. Pat. No. 3,898,253) or involve multistep synthesis (U.S. Pat. Nos. 3,646,166 and 4,173,695). Additionally, in most cases there was not an excellent retention of the original physical properties.
Polymer nanocomposites is a rapidly expanding, multidisciplinary field that represents a radical alternative to conventional-filled polymers or polymer blends. Polymer nanocomposites are formed by the incorporation of nanosized inorganic fillers into a polymer matrix. Hybrid materials reinforced with neat and/or organically modified high aspect ratio plate-like fillers represent the most widely studied class of nanocomposites. Strong interfacial interactions between the dispersed layers and the polymer matrix lead to enhanced mechanical and barrier properties over the conventional composite. Maximizing high aspect ratio fillers to their highest potential requires the correct morphology, making the selection of both the polymer and the filler critical. Polymer intercalation into the platelet galleries, delamination and exfoliation of the platelet and the anisotropic alignment of plates in the rubber matrix must be achieved. In order to accomplish at the very least the intercalation and delamination, it is advantageous to establish a chemical link between the polymer matrix and the filler surface.
U.S. application Ser. No. 11/88,172 discloses polymers, polymer compounds and composite articles made therefrom comprising maleic anhydride grafted butyl polymers and montmorillonite having surprising adhesive properties. And PCT/CA/200700425 discloses a polymerization process for preparing silica-filled butyl rubber polymers wherein quaternary onium-ion substituted nanoclays are dispersed in the organic polymerization fluid prior to initiating polymerization.